(a) Field of the Invention
This invention relates to image pickup devices and image processing systems for providing excellent images in equipment requiring high reliability and often used under low color rendering lighting, such as vehicle-mounted cameras.
(b) Description of the Related Art
As on-vehicle systems for enhancing the safety of running vehicles, a large number of systems have been conventionally proposed in which a vehicle is equipped with an image pickup means, such as a video camera, to monitor video images around the vehicle.
Specifically, such systems include visual recognition support systems for showing outputs from cameras incorporated in door and side mirror assemblies on a video display placed near the driver's seat in a vehicle to make it possible for the driver to easily check circumstances of an oncoming car and adjacent lanes and side blind spots, and recognition systems for processing a captured video signal to detect movements of surrounding cars and then give the driver an alarm depending upon distance or speed or to scan the specific regions where road signs should exist to recognize them.
The vehicle-mounted cameras used in such on-vehicle systems are required to be insusceptible to climate conditions. For example, Published Japanese Patent Application No. H05-294183 discloses, for the purpose of providing an image pickup device insusceptible to climate conditions, a technique in which the mirrors of door mirror assemblies have a half-mirror surface, the door mirror assemblies contain an optical filter-mounted video lens and an image pickup device, such as a CCD, and a video signal processed by a camera signal processing circuit disposed in the vehicle cabin is output to a video display.
The above Published Japanese Patent Application further describes that the proposed technique also solves the following problems with camera mounting positions: (1) if the camera is disposed in the cabin, this may deteriorate the beauty and comfort of the cabin and narrow the driver's scope; (2) if it is disposed in the engine room, extremely bad surrounding conditions may incur its failures; and (3) if it is disposed on the vehicle exterior, such as on door outside surfaces or the engine room, this has adverse effects on vehicle safety, design and performances such as aerodynamic resistance.